Dewaxing mineral oils



United States Patent DEWAXIN G RAL OILS Hendrik Mondria, Amsterdam,Netherlands, assignor to Shell Development Company, Emeryville, Calif.,a corporation of Delaware No Drawing. Application November 12, 1952,Serial No. 320,130

Claims priority, application Netherlands December 21, 1951 9 Claims.(Cl. 19618) This invention relates to a method of dewaxing waxy mineraloils or fractions thereof.

It has already been proposed to dewax wax-containing hydrocarbon oils,e. g., waxy mineral oils or fractions thereof, by contacting thesewax-containing oils, preferably admixed with a suitable dewaxingsolvent, at dewaxing temperatures, with an auxiliary polar liquid whichis substantially immiscible with the waxy oil preferably an aqueousliquid, containing a suitable surfaceactive agent and, if necessary, ademulsifying agent, under such circumstances that the wax passes intothis auxiliary liquid. The oil phase is then separated from theresulting wax-containing auxiliary liquid, and the wax is then recoveredfrom the auxiliary liquid phase. Separation of the wax from theauxiliary liquid is generally accomplished by removing as much of theauxiliary liquid as possible by filtration. The resulting wax phase isstill contaminated with a considerable amount of the auxiliary liquid.For example, when filtering the wax from the wax-containing auxiliaryliquid phase, a spongelike cake of wax is obtained, the water content ofwhich may be several times that of the wax. The wax is usually removedfrom the remaining auxiliary liquid by heating the mixture to atemperature (about 70 C.) at which the wax liquefies. Two immiscibleliquid phases, which can be readily separated, as by decanting, areformed. This heating operation, however, requires a considerable amountof energy, since a highly polar liquid, and particularly water,possesses a high specific heat. Furthermore, before recirculation of theseparated auxiliary liquid to the above-described dewaxing operation, itmust be cooled to the dewaxing temperature.

It is, therefore, a principal object of the present invention to providean improved method of dewaxing mineral oils. Another object of thepresent invention is to provide an improved method of dewaxing mineraloils according to the above-outlined procedure wherein a saving ofenergy is achieved in the separation of the wax from the wax-containingauxiliary liquid phase. Other objects and advantages will becomeapparent from the following detailed description.

- In accordance with the present invention, it has been found that in amethod of dewaxing waxy oils wherein the waxy oil, preferably inadmixture with a suitable dewaxing solvent, is contacted with asubstantial proportion of a substantially polar auxiliary liquid whichis substantally immiscible therewith, and with a minor amount of asuitable surface-active agent at dewaxing temperatures and under suchconditions that solid wax is preferentially wetted by the auxiliaryliquid and thereby is transferred thereto, and the oil phase is thenseparated from the resulting wax-containing auxiliary liquid phase, theforegoing objects can be achieved by contacting the wax-containingauxiliary liquid phase with an organic liquid which is substantiallyless polar than the auxiliary liquid and substantially immiscibletherewith under such conditions that the contact angle of the solid theorganic liquid phase is less than whereby the solid wax is transferredto the organic liquid phase.

Described in greater detail, the dewaxing method of the presentinvention comprises: (a) mixing the waxy oil with a substantialproportion of a dewaxing solvent which is a solvent for oil but issubstantially a non-solvent for solid wax; (b) adjusting the temperatureof the resulting mixture to obtain solid wax; (c) commingling theresulting oil-solvent phase containing solid wax dispersed therein witha substantial proportion of a substantially polar auxiliary liquid whichis substantially immiscible therewith and which has a dielectricconstant higher than that of the oil-solvent phase, and with a minoramount of a surface-active agent (preferably an ionic surface-activeagent); (d) correlating the dielectric constants of the two liquidphases so that the contact angle of the solid wax in the oil-solventphase has a value of at least about 90, preferably at least aboutwhereby the solid wax is preferentially wetted by the auxiliary liquidphase and thereby is transferred thereto; (e) separating the oil-solventphase from the resulting wax-containing auxiliary liquid phase; (f)commingling the wax-containing auxiliary liquid phase with a substantialproportion of an organic liquid which is substantially less polar thanthe auxiliary liquid, preferably a substantially non-polar organicliquid, and which is substantially immiscible with the auxiliary liquid,under such conditions that the contact angle of the solid wax in theorganic liquid is less than 90 whereby the solid wax is transferred tothe organic liquid; (g) separating the resulting wax-containing organicliquid phase from the polar auxiliary liquid; and (h) recovering waxfrom the wax-containing organic liquid. The separated polar auxiliaryliquid can be recirculated for contact with further portions of solidwax-containing oil-solvent phase.

The contact angle, generally represented by the symbol 6', is the anglewhich the interfacial tension of the two liquid phases, represented by7, forms with the solid wax.

An organic solvent is generally employed in the abovedescribed dewaxingoperation. The organic solvent used should be a good dewaxing solvent,that is, it should be a good solvent for oil, but substantially anon-solvent for solid wax. Suitable dewaxing solvents includehalogenated hydrocarbons such as ethylene dichloride, ethylenedibromide, chloroform, carbon tetrachloride, ethyl chloride, propylchloride, ethyl bromide, propyl bromide, trichloroethane,tetrachloroethane, propylene chloride, trimethylene chloride, amylbromide, tertiary amyl chloride, butyl chloride, butyl bromide, allylbromide, beta,- beta'-dichlorodiethyl ether, chlorobenzene,bromobenzene, o-dichloro-benzene, tctrachloroethylene,tetrafiuoroethylene, 2-chlorophenylamine, 3-chlorophenylamine, andl-amino-Z-fluorobenzene, aliphatic and aromatic hydrocarbons such aspetroleum ether, petroleum naphtha, gasoline, pentane, isopentane,hexane, heptane, octane, benzene, propylbenzene, cumene, amylbenzene,toluene, xylene, and cymene; ketones such as methyl isopropyl ketone,methyl isobutyl ketone, methyl ethyl ketone and mixtures thereof withhydrocarbons such as benzene and/ or toluene; and other compounds suchas nitrobenzene, furfural, aniline, toluidine, o-aminoethylbenzene,m-aminoethylbenzene, N-methylaniline, N ethylphenylamine,p-methoxy-aniline, l-ethoxybutane, and methyl phenyl ether as well asvarious mixtures thereof, and with other solvents.

It is preferred that the dielectric constant of the oil-solvent phasebefrom about 2 to about 15, and preferably from about 3 to about 10.

The solvent is employed in the ratio of from about 3 to about 10 partsby Weight of solvent to 1 part of oil.

The auxiliary liquid employed should have a higher dielectric constantthan the oil phase and should be substantially immiscible therewith. Ingeneral, the auxiliary liquid should be strongly polar in character.Water, or an aqueous liquid is, therefore, preferred. As a rule, atleast 50% of the auxiliary liquid consists of water. Lower alcohols,glycol or glycerol can be used alone as the auxiliary liquid, butcombinations thereof with water are generally preferred. In order tolower the freezing point of water, salts, such as NaCl or CaClz, oralcohols, such as methyl or ethyl alcohol or ethylene glycol, can beadded. The amount of auxiliary liquid employed should be sufficient toenable it to readily absorb the wax particle. The volume ratio ofauxiliary liquid to oil phase should be at least 1:1, preferably in therange of from about 1:1 to about 3:1.

It is preferred that the auxiliary liquid phase have a pH value ofgreater'than 7 since the contact angle increases as the pH of theauxiliary liquid phase increases. Furthermore, a pH of greater than 7promotes the formation of the more desirable oil-in-water emulsion(which is temporary) rather than a water-in-oil emulsion. The pH valueof the auxiliary liquid phase can be adjusted, for example, by theaddition of a minor amount of a basic substance such as an aqueoussodium hydroxide solution.

The surface-active agent must be selected so that, together with thecorrect adjustment of the dielectric constants of the two liquid phases,the contact angle of the solid wax in the oil phase is greater than 90.The surface-active agent can be added to either the oil phase or theauxiliary liquid. It is preferred that the surfaceactive agent besoluble in the auxiliary phase since the auxiliary phase isgenerallyrecirculated. Either anionic or cationic surface-active agentscan be used. Preferred surface-active agents are those which contain oneor more alkyl radicals having 8 or more carbon atoms connected to astrongly polar group.

Anionic type surface-active agents are represented by the aliphatic andaromatic sulfates and sulfonates, particularly alkylated aromaticsulfonates, and salts of organic compounds of phosphorus. Specificexamples include the alkali metal, particularly sodium salts of:dioctylbenzene sulfonic acid, the dioctyl ester of sulfosuccinic acid,and alkylated aryl polyether sulfate, a fatty acid ester ofsulfoacetamide, a sulfonated fatty acid amide, a mixture ofdibutylnaphthalene sulfonic acid and diisopropylnaphthalene sulfonicacid, dodecylbenzene sulfonic acid, mixtures of C9C13-benzene sulfonicacids, heptadecyl-9-sulfate, tricosanyl-lZ-sulfate,di-3,5,5-trimethylhexyl phosphate and dicotyl phosphate.

Suitable cationic surface-active agents include the quaternary ammoniumhalides, such as stearyl dirnethyl benzyl ammonium chloride.

Certain cationic agents, such as octadecylamine and dodecylamine are notsufiiciently polar to dissolve in the auxiliary liquid. By adding anacid, e. g., HCl, whereby the corresponding amine hydrochloride isformed, satisfactory results are obtained. It is preferred to add theamine to the oil phase and the acid to the auxiliary liquid.

A similar situation arises with certain anionic agents, such as oleicacid, ricinoleic acid, sulfonated ricinoleic acid ester, sulfated fattyacid esters and various naphthenic acids. Positive results can beobtained with these agents by the addition of NaOH, preferably to theauxiliary liquid.

The surface-active agent is employed in the range of from about 0.01% toabout preferably from about 0.02% to about 2%, based on the auxiliaryliquid.

Owing to the presence of the surface-active agent, the variousinterfacial tensions have become so small that the formation ofemulsions can be expected in many cases. The formation of emulsions isin itself not a disadvantage as it causes intimate contact between thewater and oil phases. For the subsequent separation of the solid wax andthe separation of the liquid phasesfrom each other it is, however,necessary that no stable emulsions be formed. It has been found that theaddition of a demulsifier will 4 prevent the formation of persistentemulsions without harming the activity of the surface-active agent. Thedemulsifier used must not, of course, precipitate the surface-activeagent.

When using an anionic surface-active agent, cationic demulsifiers aregenerally used. Suitable cationic demulsifiers are salts of polyvalentmetals, preferably divalent metals, e. g., MgSOr, MgClz, CaClz,Ni(NOs)2,Zn(NO3.).2, F6804, CuSOr, CdClz and MnSO4. Certain monovalentmetal salts, such as the lithium and ammonium salts can be used, forexample, LiCl and NH4C1.

When using a cationic surface-active agent, an anionic demulsifiershould be used. Preferred anionic demulsifiers are salts of monovalentcations and polyvalent anions, such as N212SO3, K2CrO4, Na4P2O-1,Na2SO4, NazCOs, KzCOs, K25, and NazSzOa.

Organic demulsifiers produce no results by themselves, but are activewhen used together with an inorganic salt such as sodium sulfate.Suitable organic demulsifiersinclude cyclohexylamine, phenol,diphenylamine, amyl alcohol, dodecyl alcohol, and cyclohexanol.Non-ionic surface-active agents are also active as demulsifiers whenused with an inorganic salt such as sodium sulfate. Representativenon-ionic surface-active agents include esters and ethers of polyhydroxyalcohols, particularly polyglycols, e. g., the monostearate andmonoleate of polyethylene glycol, polyoxyethylene derivatives of alkylphenols, and polyoxyethylene derivatives of sorbitol esters of fattyacids.

The demulsifier is employed in the range of about 0.0005% to about 1%,by weight, based on the auxiliary liquid.

The method of dewaxing waxy oils by transfer of solid waxv from an oilphase to an auxiliary liquid phase, and the principles on which thismethod is based are described in greater detail in the copendingapplication of Mondria et 211., Serial No. 262,438, filed December 19,1951.

The organic liquid employed in the separation of the solid wax from theauxiliary liquid in accordance with the principles of the presentinvention should be substantially less polar than the auxiliary liquidand substantially immiscible therewith. Substantially non-polar organicliquids, such as hydrocarbons, are preferred. It is also preferable touse a relatively low boiling organic liquid, that is, One boiling belowabout 125 C., and preferably below about 100 C., so that the wax canreadily be separated therefrom by distillation. The most suitableorganic liquids are hydrocarbons having less than about 10 carbon atomsper molecule, preferably less than about 8 carbon atoms per molecule,and particularly the lower alkanes, such as propane, butane, pentane,hexane, and heptane, and the relatively low boiling aromatics, such asbenzene and toluene. The lower molecular weight aliphatic ketones, suchas methyl ethyl ketone and methyl isobutyl ketone, can also be employed.It is preferred to saturate the organic liquid with wax prior toadmixture thereof with the solid wax-containing auxiliary liquid tosubstantially prevent dissolution of the solid wax in the organicliquid.

In order that the solid wax be transferred from the polar auxiliaryliquid to the substantially less polar organic liquid, it is necessarythat the contact angle of the solid wax in the organic liquid be lessthan This condition can be satisfied by suitably selecting the organicliquid, by adjusting the pH value and/ or the temperature of theauxiliary phase, by changing the nature and/ or the quantity of theauxiliary phase and/or by changing the quantity and/ or the nature ofthe surface-active substance present in the auxiliary phase. The mostattractive method of operation, particularly in a continuous operation,is to meet the above condition by suitably selecting the organic liquidso that the wax is immediately transferred from the polar auxiliaryliquid to the less polar organic liquid. By selecting a non-polarorganic liquid such as the hydrocarbons described, the Wax isimmediately transferred from the polar auxiliary liquid to the non-polarorganic liquid without any changes or adjustments in the nature of themixture.

In practice, the solid wax-containing auxiliary liquid phase obtainedfrom the above-described dewaxing operation is suitably mixed with asubstantial proportion, for example, from about 100% to about 500% byweight, based on the waxy oil charge stock, of the less polar organicliquid. If desired, a portion of the auxiliary liquid can be removed, asby decanting or by filtration, from the wax-containing auxiliary liquidphase prior to the admixture with the less polar organic liquid. Theorganic liquid employed is preferably at the same temperature as thesolid wax-containing auxiliary liquid phase. Two liquid phases areformed, the wax having merged into the organic liquid phase. The polarauxiliary liquid is readily separated from the wax-containing organicliquid, as by decantation. The separated polar auxiliary liquid phase isgenerally recycled for contact with further portions of solidwax-containing oil-solvent phase as described above. Since the auxiliaryphase has not been heated, no cooling is required prior to recycling.The wax is readily recoverable from the organic liquid by distillation,if desired, after removal of a portion of the organic liquid, as bydecantation or filtration. The separated organic liquid can be recycled,after cooling to the desired temperature, for contact with furtherportions of solid wax-containing auxiliary liquid phase.

By the practice of the present invention, it is possible to avoidfiltration entirely, while at the same time, conserving a considerableamount of energy heretofore consumed in heating the wax-containingauxiliary liquid phase to a temperature at which the wax liquefies and,after separation of the wax from the auxiliary liquid, in cooling theseparated auxiliary liquid to dewaxing temperatures for recirculation tothe dewaxing step. Furthermore, there is loss of surface-active agent.Substantially all of the surface-active agent adsorbed on the parafiinwax crystals remains in or reenters into the auxiliary liquid. Thus,substantially all of the surface-active agent employed in the dewaxingoperation can be recycled directly to the dewaxing step together withthe separated auxiliary liquid.

The following examples serve to illustrate the process of the presentinvention:

Example I A distillate from an Indonesian crude oil was diluted at atemperature of about 70 C. with about 300% by weight, based on the waxydistillate, of ethylene dichloride, and the mixture was subsequentlyslowly cooled (in about 45 minutes), with stirring, to a temperature ofabout 20 C. The resulting slurry was mixed with about 400% by weight,based on the waxy distillate, of water containing about 0.027% by weightof sodium dodecyl benzene sulfonate (propylene tetramer) and about 0.8%by weight of NaOH. The mixture was permitted to settle, and two sharplydivided phases were obtained, an oil-ethylene dichloride phase and asolid wax-containing aqueous phase. After separation of the oil-ethylenedichloride phase, the solid wax-containing aqueous phase was stirred forabout /2 minute with about 300% by Weight, based on the waxy distillate,of pentane maintained at 20 C. and saturated with solid paraflin wax asthe less polar organic liquid. The mixture was permitted to settle, andtwo phases were formed, an aqueous phase and a solid wax-containingpentane phase. A major portion of the pentane was removed by decanting,and the remainder was removed by distillation. The separated pentane canbe recycled for admixture with further portions of solid wax-containingaqueous phase.

Similar results can be obtained with the use of a reduced amount ofpentane, for example with about 150% by weight, based on the waxydistillate.

Example 11 Example III A slurry of solid wax in a mixture of oil andethylene dichloride obtained in the same manner as described in ExampleI, was mixed with stirring for about A2 minute with about 400% by weightbased on the waxy distillate, of water containing about 0.1% by weightof sodium dodecyl benzene sulfonate (propylene tetramer) assurface-active agent, about 0.16% by weight of NaOH, and about 0.01% byweight of MgSO4 as demulsifier. The mixture was permitted to settle, andtwo phases were obtained. The wax had been transferred to the aqueousphase. After separation of the oil-ethylene dichloride phase therefrom,the solid wax-containing aqueous phase was stirred for about /2 minutewith about 300% by weight, based on the waxy distillate, of n-heptanemaintained at about 20 C. and saturated with solid wax. The mixture waspermitted to settle, and two sharply divided phases were formed, anaqueous phase and a solid wax-containing n-heptane phase. Afterseparation of the aqueous phase, the wax was separated from then-heptane by decantation, followed by distillation.

I claim as my invention:

1. In a method of dewaxing a waxy mineral oil, the combination of stepscomprising: (1) mixing the waxy mineral oil with a substantialproportion of a dewaxing solvent which is a solvent for the mineral oilbut which is substantially a non-solvent for solid wax, and adjustingthe temperature of the mixture to obtain a single liquid phase of thesolvent, oil and wax; (2) cooling the mixture to a dewaxing temperatureat which the wax solidifies, thereby forming a dispersion of solid waxparticles in a liquid oil phase which is a solution of the oil and thesolvent; (3) intimately mixing the resulting dispersion of solid waxdispersed in the oil phase with a substantial proportion, at least equalin volume to the volume of the oil phase, of a substantially polarauxiliary liquid which is substantially immiscible therewith and whichhas a dielectric constant higher than that of the oil phase, theauxiliary liquid being essentially at the dewaxing temperature, and witha minor amount of a surface-active agent, whereby two liquid phasesresult, an oil phase consisting essentially of mineral oil and solventand an auxiliary liquid phase containing dissolved said surface-activeagent, and correlating the dielectric constants of the two liquid phasesso that the contact angle in the oil phase is at least whereby the solidwax is preferentially wetted by the auxiliary liquid phase and istransferred thereto to produce a dispersion of the solid wax in theauxiliary liquid phase as continuous phase, while the oil phase issubstantially freed from solid wax; (4) stratifying and separating theoil phase from the auxiliary liquid phase containing the dispersion ofsolid wax; (5) commingling the wax-containing auxiliary liquid phasewith an organic liquid, which is substantially less polar than saidauxiliary liquid and is substantially immiscible therewith, underconditions such that the contact angle of the solid wax in the organicliquid phase is less than 90", whereby the wax is transferred to saidorganic liquid phase; and (6) stratifying and separating the organicliquid phase containing the wax dispersed therein from the auxiliaryliquid phase.

2. The method according to claim 1, wherein the organic liquid is asubstantially non-polar organic liquid.

3. The method according to claim 1, wherein the organic, liquid" is; a;substantially non-polar" organic liquid havingza: boiling point belowabout 125 C..

4-, The method. according to claim 1, wherein the auxiliary liquid. is asubstantially aqueous liquid, and wherein the organic liquid is asubstantially non-polar organic liquid havinga boiling point-below about125 C.

5-. The method accordingv to: claim l,v wherein the auxiliary liquid isa substantially aqueous liquid, wherein the surface-active agent isanionic surface-activev agent, and wherein the organic liquid is asubstantially non-polar organic liquid having a boiling point belowabout 125 C.

6. The method according to claim 1, wherein the auxiliary liquid is asubstantially aqueous liquid, wherein theisurface-active agent is anionic surface-active agent, andwherein the organic liquid is ahydrocarbon having aboiling point below about 125 C.

References Citedinthe file of this patent UNITED STATES PATENTS Carr etal. Nov. 18, 1941 Myers et al. July 14, 1953

1. IN A METHOD OF DEWAXING A WAXY MINERAL OIL, THE COMBINATION OF STEPS COMPRISING: (1) MIXING THE WAXY MINERAL OIL WITH A SUBSTANTIAL PROPORTION OF A DEWAXING SOLVENT WHICH IS A SOLVENT FOR THE MINERAL OIL BUT WHICH IS SUBSTANTIALLY A NON-SOVENT FOR SOLID WAX, AND ADJUSTING THE TEMPERATURE OF THE MIXTURE TO OBTAIN A SINGLE LIQUID PHASE OF THE SOLVENT, OIL AND WAX; (2) COOLING THE MIXTURE TO A DEWAXING TEMPERATURE AT WHICH THE WAX SOLIDIFIES, THEREBY FORMING A DISPERSION OF SOLID WAX PARTICLES IN A LIQUID OIL PHASE WHICH IS A SOLUTION OF THE OIL AND THE SOLVENT; (3) INTIMATELY MIXING THE RESULTING DISPERSION OF SOLID WAX DISPERSED IN THE OIL PHASE WITH A SUBSTANTIAL PROPORTION, AT LEAST EQUAL IN VOLUME TO THE VOLUME OF THE OIL PHASE, OF A SUBSTANTIALLY POLAR AUXILIARY LIQUID WHICH IS SUBSTANTIALLY IMMISCIBLE THEREWITH AND WHICH HAS A DIELECTRIC CONSTANT HIGHER THAN THAT OF THE OIL PHASE, THE AUXILIARY LIQUID BEING ESSENTIALLY AT THE DEWAXING TEMPERATURE, AND WITH A MINOR AMOUNT OF A SURFACE-ACTIVE AGENT, WHEREBY TWO LIQUID PHASES RESULT, AN OIL PHASE CONSISTING ESSENTIALLY OF MINERAL OIL AND SOLVENT AND AN AUXILIARY LIQUID PHASE CONTAINING DISSOLVED SAID SURFACE-ACTIVE AGENT, AND CORRELATING THE DIELECTRIC CONSTANTS OF THE TWO LIQUID PHASES SO THAT THE CONTACT ANGLE IN THE OIL PHASE IS AT LEAST 90*, WHEREBY THE SOLID WAX IN THE AUXILIARY BY THE AUXILIARY LIQUID PHASE AND IS TRANSFERRED THERETO TO PRODUCE A DISPERSION OF THE SOLID WAX IN THE AUXILIARY LIQUID PHASE AS CONTINUOUS PHASE, WHILE THE OIL PHASE IS SUBSTANTIALLY FREED FROM SOLID WAX; (4) STRATIFYING AND SEPARATING THE OIL PHASE FROM THE AUXILIARY LIQUID PHASE CONTAINING THE DISPERSION OF SOLID WAX; (5) COMMINGLING THE WAX-CONTAINING AUXILIARY LIQUID PHASE WITH AN ORGANIC LIQUID, WHICH IS SUBSTANTIALLY LESS POLAR THAN SAID AUXILIARY LIQUID AND IS SUBSTANTIALLY IMMISCIBLE THEREWITH, UNDER CONDITIONS SUCH THAT THE CONTACT ANGLE OF THE SOLID WAX IN THE ORGANIC LIQUID PHASE IS LESS THAN 90*, WHEREBY THE WAX IS TRANSFERRED TO SAID ORGANIC LIQUID PHASE; AND (6) STRATFYING AND SEPARATING THE ORGANIC LIQUID PHASE CONTAINING THE WAX DISPERSED THEREIN FROM THE AUXILIARY LIQUID PHASE. 